Coordinately unsaturated metal excitation

Weitz and co-workers extended gas phase TRIR investigations to the study of coordinatively unsaturated metal carbonyl species. Metal carbonyls are ideally suited for TRIR studies owing to their very strong IR chromophores. Indeed, initial TRIR work in solution, beginning in the early 1980s, focused on the photochemistry of metal carbonyls for just this reason. Since that time, instrumental advances have significantly broadened the scope of TRIR methods and as a result the excited state structure and photoreactivity of organometallic complexes in solution have been well studied from the microsecond to picosecond time scale. ... 

BCPDA is a tetradentate ligand, and forms 1 1 complexes in these conditions. The metal ion is thus coordinatively unsaturated, and also binds a number of water molecules, which can lead to non-radiative quenching of the metal-centered excited state (vide supra). These must be removed by drying to achieve optimal luminescence intensity. This form of assay is, in fact, slightly less sensitive than DELFIA. 

The second photochemical reaction which was studied was the reaction of CotCO NO with Lewis base ligands L (J 6 ). The observed solution phase photochemical reaction is carbonyl photosubstitution. This result initially did not appear to be related to the proposed excited state bending. Further reflection led to the idea that the bent molecule in the excited state is formally a 16 electron coordinatively unsaturated species which could readily undergo Lewis base ligand association. Thus, an associative mechanism would support the hypothesis. Detailed mechanistic studies were carried out. The quantum yield of the reaction is dependent on both the concentration of L and the type of L which was used, supporting an associative mechanism. Quantitative studies showed that plots of 1/ vs. 1/[L] Were linear supporting the mechanism where associative attack of L is followed by loss of either L or CO to produce the product. These studies support the hypothesis that the MNO bending causes a formal increase in the metal oxidation state. 

Metal ion can form complex through coordination with unsaturated compounds such as olefin. Through coordination with metal ion, two olefins can be positioned in close proximity, and olefin photochemistry may be caused upon irradiation at longer wavelengths by exciting the charge-transfer band of the resultant complex. Evers and Mackor investigated the intramolecular [2-h2] photocycloaddition of diene 148, which is photochemi-cally catalyzed by copper(l) trifluoromethanesulphonate. In the presence of the copper... 

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